The present invention relates to the field of microwave integrated circuits, and more particularly to a device for achieving conversion of a microstrip transmission line mode ("microstrip") to a slot transmission line ("slotline") mode with transmission lines existing on one side of a substrate.
Microwave integrated technology includes devices such as a microstrip and a slotline. A microstrip is an unbalanced, wideband transmission line which is easily manufactured, and generally comprises a thin conductor layer on one surface of an insulating substrate, generally formed by well known printed circuit techniques, and a wider ground plane conductor joined to the opposite side of the insulating substrate. A slotline is a balanced transmission line and generally comprises a slot formed between electrically conductive coatings formed on an insulating substrate. In the operation of a slotline, there is generally a voltage difference between the edges of the slot. The voltage difference generates an electric field which extends across the slot and a magnetic field which is perpendicular to the electric field. Because the voltage difference extends across the slot, a slotline is especially convenient for connecting shunt elements such as diodes, resistors, and capacitors across the slot.
Devices for converting radio frequency (RF) energy from a microstrip transmission mode to a slotline transmission mode are well known. With such devices, the microstrip and slotlines are usually located on opposite sides of an insulating substrate. Unfortunately, these devices are not easily implemented in microwave integrated circuits (MIC) or monolithic microwave integrated circuits (MMIC) which require that the circuit be suspended because circuit elements are typically mounted on both sides of the substrate and would otherwise be shorted out.
Therefore, there is a need for a microwave to slotline transition in which the circuit elements are fabricated on one side of a substrate in order to simplify their manufacture and to facilitate their integration into microwave integrated circuits by allowing one side to be grounded to a metal shielding structure.